P.S. I also have a follow-up question:
quam angusta innocentia est ad legem bonum esse! (De Ira, 2.28.2)
You already told me the meaning of this sentence. The thing I am still not clear is the grammatical function of "ad legem bonum esse" and especially the inf. "esse" confuses me.

AnswerDear Robert,

1.In “….aut fortasse ipsum hoc meritum eius est quo offendimur..” (Seneca, De Ira, 2.30.1) the neuter singular “ipsum hoc” which refers to “quo “ in “quo offendimur” is the subject of the verb “est”.
As for “eius”, it goes with “meritum” in the sense that “….ut fortasse ipsum hoc meritum eius est quo offendimur” literally means:
" …or maybe (aut fortasse) this same thing (ipsum hoc, subject) by which (quo) we feel offended (offendimur) is his (eius) merit/service (meritum, predicate noun)..”, just to emphasize that just the act which offends us is really a service of our father because our father has been so good to us that he has even the right to injure us.

2.In “….levius transiliet sustinentem …”(De Ira, 2.30.2) the present participle in the accusative singular “sustinentem” depends on “transiliet” whose subject is the preceding “morbus” or “calamitas” in “Morbus est aut calamitas”(Is it a sickness or a misfortune) so that “..levius transiliet sustinentem” literally means:
”... it (i.e.sickness or misfortune) will get over (transiliet) more lightly (levius) the one who endures (sustinentem) [them]”, just to point out that a sickness or a misfortune will pass more easily if we are able to bear up them.

3. In “….regis quisque intra se animum habet, ut licentiam sibi dari uelit, in se nolit” (De Ira, 2.31.3)the phrase “in se nolit” means:” he does not want (nolit) [that licence is permitted/ licentiam dari] against himself (in se)”.
As you can see, “in se nolit” implies “licentiam dari”, since the one who feels like a king thinks that he himself can use any license against everyone, whereas nobody must use the same licence against himself.

4.In “…quia singula servari totius interest..” (De Ira, 2.31.7) the substantive clause “singula servari” is the subj. of the verb “interest”, while the genitive “totius” denotes the thing affected, just because the impersonals "interest and rēfert" take the Genitive of the person (or of the thing) affected, while the subject of the verb is a neuter pronoun or a substantive clause (See AG 355).
In short, “…quia singula servari totius interest..” literally means:
”.. for (quia) it is the interest (interest) of the whole (totius) the fact that every part (singula, neuter plural) is preserved (servari)”, with reference to the fact that all the members of the body must be in harmony one with another because everybody’s safety is the interest of the whole.

Best regards,

Maria
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P.S.
In “….quam angusta innocentia est ad legem bonum esse!” (De Ira, 2.28.2) the infinitive “esse” with the preceding predicate adjective “bonum” is a subject-clause of the verb “est” so that the literal translation would be “..to be (esse) good (bonum) according to (ad) law (legem) is (est) a very small (angusta) innocence (innocentia” as well as “….how (quam) small/limited (angusta, adjective in the nominative feminine agreeing with “innocentia”) innocence (innocentia) is to be (esse) good (bonum) according to (ad)
law (legem)!”, as I’ve already said.

Note that in "bonum esse" the predicate adjective is in the accusative because in the subject-clause the infinitive requires the accusasative of a predicate adjective or predicate noun.